This application claims priority to Japanese Patent Application No. P2001-370612 filed on Dec. 4, 2001, the contents of which are hereby incorporated by reference.
The present invention relates to a spatial light modulator for spatially modulating incident light by utilizing a magneto-optic effect.
A spatial light modulator for spatially modulating incident light is used in the field of optical information processing computer-generated holograms or the like.
Conventional spatial light modulators include one in which a liquid crystal is used and one in which a micro-mirror device is used.
In the above-mentioned field of optical information processing, computer-generated holograms or the like, it is necessary that a large amount of information be processed at high speed, and therefore it is desirable that the spatial light modulator should have a high operation speed.
However the spatial light modulator in which a liquid crystal is used has a low operation speed. For example, even in the case of using a ferroelectric liquid crystal that has a high operation speed among liquid crystals the response time is on the order of microsecond.
The spatial light modulator in which a micro-mirror device is used can operate at a relatively high speed. However, the manufacturing cost for this spatial light modulator is high because it is a micro machine having a complicated structure which is manufactured by a highly-developed semiconductor manufacturing process. Moreover, there remains a problem in reliability because it has a mechanical driving portion.
For example, U.S. Pats. No. 4,584,237, No. 5,241,421, No. 5,255,119 and No. 5,386,313 disclose spatial light modulators for modulating incident light by utilizing a magneto-optic effect. Hereinafter, such a spatial light modulator is referred to as a magneto-optic spatial light modulator. The magneto-optic spatial light modulator includes a plurality of pixels, each of which is made of a magneto-optic material and capable of selecting a direction of magnetization independently. In the magneto-optic spatial light modulator, a direction of polarization of light passing through each pixel is rotated by a predetermined angle in a direction opposite to the direction of magnetization of the pixel due to the Faraday effect. Accordingly, the magneto-optic spatial light modulator produces spatially modulated light by arbitrarily selecting a direction of magnetization for each pixel.
Since the magneto-optic spatial light modulator exhibits a high speed in reversing the direction of magnetization of each pixel, it can achieve a higher operation speed on a pixel-by-pixel basis than that of a spatial light modulator in which a liquid crystal is used.
In a conventional magneto-optic spatial light modulator, the magnetic layer is completely divided into a plurality of portions, each of which makes up a pixel.
In the conventional magneto-optic spatial light modulator, two kinds of conductors are arranged in the form of a grid so as to intersect each other at positions of individual pixels. When a direction of magnetization of any one of the pixels is to be reversed, a current is passed through the two conductors intersecting each other at the position of that pixel, so that a magnetic field for reversing the direction of magnetization of that pixel is produced.
The conventional magneto-optic spatial light modulator has a problem that the reversal of directions of magnetization of the pixels requires a high magnetic field and accordingly a high driving current.
For the conventional magneto-optic spatial light modulator, in order to enhance the Faraday effect to improve magneto-optic performance, it is necessary to increase the thickness of the magnetic layer. Besides, in the conventional magneto-optic spatial light modulator, grooves are formed between adjacent pixels to completely divide the magnetic layer into pixels. For this reason, in the conventional magnetic layer is increased, it becomes necessary to increase the depths of the grooves formed in the magnetic layer as well.
This makes it difficult to form the grooves. Moreover, if the depths of the grooves are increased, it becomes impossible to form the conductors on the magnetic layer without being processed. Therefore, to form the conductors on the magnetic layer, it is necessary to fill the grooves with an insulating material and then to flatten the top surface of the magnetic layer. In addition, if the depths of the grooves are increased, it becomes technically difficult to fill the grooves with an insulating material and to flatten the top surface of the magnetic layer.
It is an object of the invention to provide a spatial light modulator for spatially modulating incident light by utilizing a magneto-optic effect which is simple in structure and easy to drive.
A spatial light modulator of the invention comprises:
a magnetic layer made of a magneto-optic material and including a plurality of pixels whose directions of magnetization are set independently of one another, each of the pixels causing rotation of a direction of polarization of incident light depending on its direction of magnetization due to a magneto-optic effect; and
a magnetic field generator for generating a magnetic field for setting the direction of magnetization of each of
the pixels of the magnetic layer wherein the magnetic layer has one surface, the other surface, and grooves for defining borders of the individual pixels, the grooves extending from the one surface to a predetermined position between the one surface and the other surface.
In the spatial light modulator of the invention, borders of the individual pixels are defined by the grooves formed to extend from the one surface of the magnetic layer to a predetermined position between the one surface and the other surface of the magnetic layer. According to the spatial light modulator of the invention, direction of magnetization of each of the pixels is set by the magnetic field generator. Then, the direction of polarization of incident light is rotated depending on the direction of magnetization of each of the pixels, whereby the incident light is modulated spatially.
In the spatial light modulator of the invention, the magnetic field generator may include a plurality of first conductor layers and a plurality of second conductor layers arranged to intersect each other at positions corresponding to the pixels, currents for generating the magnetic field for setting the direction of magnetization of each of the pixels being passed through the first and second conductor layers.
Other objects features and advantages of the invention will become sufficiently clear from the following description.